1. Field of the Invention
The present invention relates to an optical fibre connector, and particularly a connector having a receptacle or socket with a recessed optical fibre/ferrule assembly for aligning an optical fibre within the connector, and to a method of cleaning such a recessed assembly.
2. Brief Description of Related Developments
Optical devices such as optical transceiver units often have an optical port for receiving and/or transmitting laser light from/into optical fibre cables, for example as part of an optical communications system. The optical fibre cable has at its end a connector by which one or more optical fibres within the cable may be connected and disconnected to a mating connector at the port. Usually, the fibre cable connector is a male type connector feature (hereinafter referred to as an “optical plug”), which locates within a female type connector feature (hereinafter referred to as an “optical socket”), on the laser transceiver unit.
The optical transceiver unit will normally be fixed in place, for example as part of a rack of similar such transceiver units. One reason for this arrangement is to protect the exposed end of one or more optical fibres within the optical socket, either from physical damage or from dirt or dust. It is easier to repair the termination of an optical fibre cable having an optical plug than it is a transceiver unit. A damaged optical fibre cable may be recut, reassembled and polished or may have its exposed end cleaned. In contrast, an optical port may have a relatively short fibre stub which needs to be maintained in a preset alignment with other optical components, such as a photodiode detector or a laser diode source.
Another reason why it may be desirable to provide the optical socket at the transceiver unit is that an optical fibre end, which is recessed in the socket, can be made eye-safe when the cable connector is not connected to a laser transmitter port. In many cases, optical communications links operate at near-infrared wavelengths of 1.3 μm and 1.5 μm, which presents added risk because such wavelengths are invisible. Applicable eye-safety standards for infra-red laser diode transmitter units are the US Standard CDRH Class 1 and the European Standard IEC 825.
Current laser safety guidelines require that the output power density from an optical port of an optical transmitter unit be limited to a level, which is eye-safe when no fibre optic connector is connected to the port. Optical coupling efficiencies from a laser diode into an optical fibre are typically quite low, for example of the order of about 1% to 25%. Even if the amount of laser radiation transmitted by the fibre is eye-safe, the total amount of optical radiation emitted by the laser diode may far exceed the limit of eye-safety. It may therefore be necessary either to block unwanted light within the port, or to defocus stray light emitted by the port when no optical connector is connected to the port.
One type of optical socket which addresses this problem is disclosed in patent document U.S. Pat. No. 5,315,680, the contents of which are incorporated herein by reference, which describes an optical port having a short optical fibre stub held securely in alignment with a laser diode concealed within an optical transmitter unit. Collimating optics are used to focus the laser light into a single-mode core of the fibre. The fibre stub is typically 5 mm to 6 mm long. Light which is not coupled into the core enters the fibre optic cladding, and is dissipated by multiple reflections and scattering within the core and by the exterior surface of the cladding. Any laser radiation that exits from the cladding is not collimated, and is essentially “defocussed” so that the inherent brightness of such stray radiation is greatly reduced. Eye-safety is further enhanced by recessing the end of the optical fibre within a cylindrical housing that extends forwards of the optical fibre end and which forms an optical socket into which an optical fibre cable plug is plugged.
The optical fibres of the optical socket and optical plug are centered axially in corresponding ceramic ferrules. Alignment between the optical fibres of the optical socket and optical plug is provided by a cylindrical split sleeve in the socket which extends around and forwards of the optical socket ferrule and which grips and locates the cylindrical ferrule of the optical plug when this is inserted into the socket.
This arrangement has been known for many years, and while this does in general provide good protection to the end of the fibre stub in the optical socket, the exposed fibre end may still become contaminated with dust or dirt. Because of the recessed position of the exposed fibre end, it can be difficult to clean away such contamination in order to improve optical coupling between the optical socket and an optical plug. The conventional method for cleaning such a component is to push a cleaning swab, to which has been applied a cleaning solution, into the receptacle in order to wipe the exposed fibre end. Although this can be done satisfactorily, it is likely that the receptacle will require many attempts at cleaning, interposed with tests to see if good optical coupling has been achieved between the optical socket and the optical plug. Furthermore, it is likely that contamination will remain somewhere within the optical socket assembly.